55. Evaluate the following two queries:
SQL> SELECT cust_last_name, cust_city
FROM customers
WHERE cust_credit_limit IN (1000, 2000, 3000);
SQL> SELECT cust_last_name, cust_city
FROM customers
WHERE cust_credit_limit = 1000 OR cust_credit_limit = 2000 OR cust_credit_limit = 3000;
Which statement is true regarding the above two queries?
A. Performance would improve in query 2.
B. Performance would degrade in query 2.
C. There would be no change in performance.
D. Performance would improve in query 2 only if there are null values in the CUST_CREDIT_LIMIT
column.
Answer: C
答案解析：
sh@TESTDB> SELECT cust_last_name, cust_city
2 FROM customers
3 WHERE cust_credit_limit IN (1000, 2000, 3000);
7975 rows selected.
Elapsed: 00:00:00.07
Execution Plan
----------------------------------------------------------
Plan hash value: 2008213504
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 20556 | 441K| 406 (1)| 00:00:05 |
|* 1 | TABLE ACCESS FULL| CUSTOMERS | 20556 | 441K| 406 (1)| 00:00:05 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("CUST_CREDIT_LIMIT"=1000 OR "CUST_CREDIT_LIMIT"=2000 OR
"CUST_CREDIT_LIMIT"=3000)
sh@TESTDB> SELECT cust_last_name, cust_city
2 FROM customers
3 WHERE cust_credit_limit = 1000 OR cust_credit_limit = 2000 OR cust_credit_limit = 3000;
7975 rows selected.
Elapsed: 00:00:00.08
Execution Plan
----------------------------------------------------------
Plan hash value: 2008213504
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 20556 | 441K| 406 (1)| 00:00:05 |
|* 1 | TABLE ACCESS FULL| CUSTOMERS | 20556 | 441K| 406 (1)| 00:00:05 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("CUST_CREDIT_LIMIT"=1000 OR "CUST_CREDIT_LIMIT"=2000 OR
"CUST_CREDIT_LIMIT"=3000)
一样的执行计划，性能一样，故选C